1. Field of the Invention
The present invention relates to a piezoelectric/electrostrictive device that is provided with a movable section to be operated on the basis of a displacement action of a piezoelectric/electrostrictive element, or a piezoelectric/electrostrictive device that is capable of detecting displacement of a movable section by the aid of a piezoelectric/electrostrictive element, and a method for producing the same. In particular, the invention relates to a piezoelectric/electrostrictive device that is excellent in strength, shock resistance, and moisture resistance and that makes it possible to efficiently operate a movable section to a great extent, and a method for producing the same.
2. Background of the Invention
Recently, a displacement element, which makes it possible to adjust the optical path length and the position in an order of submicron, is demanded, for example, in the fields of optics, magnetic recording, and precision machining. Development is advanced for the displacement element based on the use of the displacement brought about by the inverse piezoelectric effect or the electrostrictive effect caused when a voltage is applied to a piezoelectric/electrostrictive material (for example, a ferroelectric material).
As shown in FIG. 26, for example, those hitherto disclosed as such a displacement element include a piezoelectric actuator comprising a fixing section 204, a movable section 206, and a beam section 208 for supporting the fixing and movable sections, which are formed integrally with a hole 202 provided through a plate-shaped member 200 composed of a piezoelectric/electrostrictive material and with an electrode layer 210 provided on the beam section 208 (see, for example, Japanese Laid-Open Patent Publication No. 10-136665).
The piezoelectric actuator is operated such that when a voltage is applied to the electrode layer 210, the beam section 208 makes expansion and contraction in a direction along a line obtained by connecting the fixing section 204 and the movable section 206 in accordance with the inverse piezoelectric effect or the electrostrictive effect. Therefore, the movable section 206 can perform circular arc-shaped displacement or rotational displacement in the plane of the plate-shaped member 200.
On the other hand, Japanese Laid-Open Patent Publication No. 63-64640 discloses a technique in relation to an actuator based on the use of a bimorph. In this technique, the electrodes of the bimorph actuator are provided in a divided manner. The actuator is driven by selecting the divided electrodes, and thus highly accurate positioning is performed at a high speed. JP ""640 discloses a structure (especially in FIG. 4) in which, for example, two opposed bimorphs are used.
However, the piezoelectric actuator described above involves a problem that the amount of operation of the movable section 206 is small, because the displacement in the direction of extension and contraction of the piezoelectric/electrostrictive material (i.e., in the in-plane direction of the plate-shaped member 200) is transmitted to the movable section 206 as it is.
Since all the parts of the piezoelectric actuator are made of piezoelectric/electrostrictive materials, which are fragile materials having a relatively heavy weight, the mechanical strength is low, and the piezoelectric actuator is inferior in handling performance, shock resistance, and moisture resistance. Furthermore, the piezoelectric actuator itself is heavy, and its operation tends to be affected by harmful vibrations (for example, residual vibration and noise vibration during high speed operation).
Then, a method may be proposed which increases the strength and the resonant frequency by thickening a beam portion, for example, in order to improve stiffness. However, displacement and a response speed are significantly deteriorated due to the improvement of stiffness.
Further, the following structure is disclosed in FIG. 4 in Japanese Laid-Open Patent Publication No. 63-64640, a joined form exists between a mediating member and a bimorph and between a head and the bimorph (i.e., so-called piezoelectric operating sections, both of which cause the strain). In other words, the bimorph is formed contiuously ranging from the mediating member to the head.
As a result, when the bimorph is operated, the displacement action, which is effected with the supporting point of the joined portion between the mediating member and the bimorph, mutually interferes with the displacement action which is effected with the supporting point of the joined point between the head and the bimorph. The expression of the displacement is inhibited. In this structure, it is impossible to obtain a function that the head is greatly displaced with respect to the external space.
The conventional device of this type has a structure which is weak against external forces in many situations. A problem arises in that it is difficult to handle the device and to achieve the realization of a high resonance frequency.
The present invention has been made taking the foregoing problems into consideration, and an object thereof is to provide a piezoelectric/electrostrictive device and a method for manufacturing the same. According to the piezoelectric/electrostrictive device of the present invention, it is possible to obtain a displacement element that is easy in handling, high in shock resistance against external forces without deteriorating the device characteristics such as the displacement characteristic and the response characteristic, and scarcely affected by harmful vibration, and that is capable of large displacement and high speed response with high mechanical strength while being excellent in moisture resistance, as well as a sensor element that makes it possible to accurately detect vibration of the movable section.
Further, an object of the present invention is to provide a piezoelectric/electrostrictive device and a method for manufacturing the same which can suppress occurrence of problems caused by unnecessary vibrations during its manufacture and improve the productivity of manufacturing the piezoelectric/electrostrictive device.
According to the present invention, a piezoelectric/electrostrictive device has a pair of mutually opposing thin plate sections, a movable section, and a fixing section for supporting the thin plate sections and the movable section, the piezoelectric/electrostrictive device includes:one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections, and
a hole is formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixing section.
A mechanism is provided for restricting amplitude of the thin plate sections. Thus, when the external force is applied to the thin plate section and the movable section, which causes their large vibration (amplitude), the mechanism can restrict the vibration (amplitude) of the thin plate section. As a result, it can prevent the thin plate section from being damaged. In this case, the thin plate section does not need to be thickened. Therefore, material characteristics of the piezoelectric/electrostrictive element provided on the thin plate section are not deteriorated, which does not correspondingly deteriorate device characteristics such as the displacement characteristic and the response characteristic.
In other words, the present invention can provide a displacement element that is easy in handling, high in shock resistance against the external force without deteriorating the device characteristics such as the displacement characteristic and the response characteristic, and is scarcely affected by harmful vibration, and that is capable of a large displacement and high speed response with high mechanical strength while being excellent in moisture resistance, as well as a sensor element that makes it possible to accurately detect vibration of the movable section.
Further, when unnecessary vibration is applied during production, the mechanism can restrict the vibration (amplitude) of the thin plate section. Therefore, damage to the thin plate section due to the unnecessary vibration can be prevented effectively, which can improve the productivity of manufacturing the piezoelectric/electrostrictive device.
The mechanism may have a cavity portion formed on the inner wall of the movable section and a stopper member provided on the inner wall of the fixing section having a forward end extending into the cavity portion. Alternatively, the mechanism may have a cavity portion formed on the inner wall of the fixing section and a stopper member provided on the inner wall of the movable section having a forward end extended into the cavity portion. In this case, when the forward end of the stopper member hits the cavity portion, vibration (amplitude) of the thin plate section is restricted thereby. Further, the appropriately adjusted length and thickness of the stopper member gives resilience to the stopper member so as to absorb shocks caused when the stopper member hits the cavity portion.
Preferably, a shortest distance from the forward end of the stopper member to an inner wall of the cavity portion in a direction of displacing the movable section is not more than a tolerance limit of amplitude of the thin plate sections. In this case, damages of the thin plate section can be prevented effectively since vibration (amplitude) of the thin plate section is not more than a tolerance limit.
The mechanism may have two buffer members formed on the inner wall of the fixing section and a stopper member provided on the inner wall of the movable section, whose forward end enters between the two buffer members. Alternatively, the mechanism may have two buffer members formed on the inner wall of the movable section and a stopper member provided on the inner wall of the fixing section, whose forward end enters between the two buffer members.
In this case, when the forward end of the stopper member hits the buffer member, vibration (amplitude) of the thin plate section is restricted thereby. Further, the appropriately adjusted aspect ratio by height and thickness of the buffer member gives resilience to the buffer member so as to absorb shocks caused when the stopper member hits the buffer member.
Furthermore, the mechanism may have a projecting portion formed from said inner wall of said fixing section into said hole, wherein a shortest distance from said projecting portion to said thin plate section is not more than a tolerance limit of amplitude of said thin plate sections. In this case, damages of the thin plate section can be prevented effectively since vibration (amplitude) of the thin plate section is not more than a tolerance limit. Especially in this arrangement, vibration (amplitude) causing a damage on the thin plate section is restricted effectively when an external force is applied to the thin plate section directly (and intensively), which is effective in preventing the damage on the thin plate section.
The movable section, the fixing section, the thin plate section, and the mechanism can be made of ceramics or metal. That is, each of the components may be made of a ceramic material, or each of them may be made of a metal material. Alternatively, each of the components may be constructed to have a hybrid structure obtained by combining those produced from materials of ceramics and metal.
The thin plate sections, the movable section, the fixing section, and the mechanism may comprise an integrated ceramic substrate formed by simultaneously firing a ceramic green laminate, followed by cutting off unnecessary portions. Further, the piezoelectric/electrostrictive elements may be of a film form and integrated with the ceramic substrate by firing.
Moreover, the piezoelectric/electrostrictive elements may have a piezoelectric/electrostrictive layer and a pair of electrodes formed on the piezoelectric/electrostrictive layer. The piezoelectric/electrostrictive element may have a piezoelectric/electrostrictive layer and a pair of electrodes formed on both sides of the piezoelectric/electrostrictive layer, and one electrode of the pair of electrodes may be formed on at least the thin plate section. In this arrangement, the vibration caused by the piezoelectric/electrostrictive element can be efficiently transmitted via the thin plate section to the movable section or the fixing section. Thus, it is possible to improve the response performance. Further, it is preferable that the piezoelectric/electrostrictive elements are constructed by laminating a plurality of the piezoelectric/electrostrictive layers and the pairs of electrodes.
According to the present invention, a method is provided for producing a piezoelectric/electrostrictive device having a pair of mutually opposing thin plate sections, a movable section, and a fixing section for supporting the thin plate sections and the movable section. The piezoelectric/electrostrictive device includes one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections, and a hole formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixing section. The method comprises the step of cutting off a predetermined portion, after forming the piezoelectric/electrostrictive elements on at least the thin plate sections, to produce the piezoelectric/electrostrictive device having a mechanism for restricting amplitude of the thin plate sections.
The phrase xe2x80x9cafter forming the piezoelectric/electrostrictive elementxe2x80x9d referred to herein indicates a state in which at least the piezoelectric/electrostrictive layer is formed on the thin plate section. As for the electrode to be formed after the formation of the piezoelectric/electrostrictive layer, the electrode may be formed after performing the cutoff on a predetermined portion.
Further, according to the present invention, a method is provided for producing a piezoelectric/electrostrictive device having a pair of mutually opposing thin plate sections, a movable section, and a fixing section for supporting the thin plate sections and the movable section, the piezoelectric/electrostrictive device including one or more piezoelectric/electrostrictive elements arranged on at least one thin plate section of the pair of thin plate sections, and a hole formed by both inner walls of the pair of thin plate sections, an inner wall of the movable section, and an inner wall of the fixing section. The method comprises the steps of producing a ceramic laminate by firing a ceramic green laminate containing first ceramic green sheets, second ceramic green sheets for constituting a mechanism for restricting amplitude of the thin plate sections and third ceramic green sheets for constituting the thin plate sections integrally, the first ceramic green sheets each having a window for forming at least the hole,
forming the piezoelectric/electrostrictive elements on a part of an outer surface of the ceramic laminate for constituting the thin plate sections; and
producing a piezoelectric/electrostrictive device having the mechanism for restricting amplitude of the thin plate sections by cutting at least once the ceramic laminate having the piezoelectric/electrostrictive element.
According to the production method, it is possible to obtain a displacement element that is scarcely affected by harmful vibration and capable of high speed response with high mechanical strength while being easy in handling performance, high in shock resistance against the external force, and excellent in moisture resistance without deteriorating the device characteristics such as the displacement characteristic and the response characteristic, as well as a sensor element that makes it possible to accurately detect vibration of the movable section.
In the production methods, the exposure of the hole can be also performed in the cutting step by cutting the ceramic laminate. In this case, the movable section (and/or fixing section) having opposing surfaces, and the hole can be made simultaneously. However, the movable section (and/or fixing section) and the hole can be made separately.
When the cut-off treatment is performed by means of machining, unnecessary vibration is applied. However, the mechanism can restrict the vibration (amplitude) of the thin plate section. Therefore, damages on the thin plate section during the manufacturing processes due to the unnecessary vibration can be prevented effectively, which can improve the productivity of manufacturing the piezoelectric/electrostrictive device.
Therefore, the piezoelectric/electrostrictive device according to the present invention can be utilized as the active device including, for example, various transducers, various actuators, frequency region functional parts (filters), transformers, vibrators, resonators, oscillators, and discriminators for the communication and the power generation, as well as the sensor element for various sensors including, for example, ultrasonic sensors, acceleration sensors, angular velocity sensors, shock sensors, and mass sensors. Especially, the piezoelectric/electrostrictive device according to the present invention can be preferably utilized for various actuators to be used for the mechanism for adjusting the displacement and the positioning and for adjusting the angle for various precision parts such as those of optical instruments and precision mechanical equipments.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.